close • man page

close - close a file descriptor

close • man page

close - close a file descriptor

close (2)

Leading comments

This manpage is Copyright (C) 1992 Drew Eckhardt;
and Copyright (C) 1993 Michael Haardt, Ian Jackson.
and Copyright (C) 2016 Michael Kerrisk <mtk.manpages@gmail.com>
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(The comments found at the beginning of the groff file "man2/close.2".)

NAME

close - close a file descriptor

SYNOPSIS

DESCRIPTION

close()
closes a file descriptor, so that it no longer refers to any file and
may be reused.
Any record locks (see
fcntl(2))
held on the file it was associated with,
and owned by the process, are removed (regardless of the file
descriptor that was used to obtain the lock).

If
fd
is the last file descriptor referring to the underlying
open file description (see
open(2)),
the resources associated with the open file description are freed;
if the descriptor was the last reference to a file which has been
removed using
unlink(2),
the file is deleted.

RETURN VALUE

close()
returns zero on success.
On error, -1 is returned, and
errno
is set appropriately.

ERRORS

CONFORMING TO

POSIX.1-2001, POSIX.1-2008, SVr4, 4.3BSD.

NOTES

Not checking the return value of
close()
is a common but nevertheless
serious programming error.
It is quite possible that errors on a
previous
write(2)
operation are first reported at the final
close().
Not checking the return value when closing the file may lead to
silent loss of data.
This can especially be observed with NFS
and with disk quota.
Note that the return value should be used only for diagnostics.
In particular
close()
should not be retried after an
EINTR
since this may cause a reused descriptor from another thread to be closed.

A successful close does not guarantee that the data has been successfully
saved to disk, as the kernel defers writes.
It is not common for a filesystem
to flush the buffers when the stream is closed.
If you need to be sure that
the data is physically stored, use
fsync(2).
(It will depend on the disk hardware at this point.)

It is probably unwise to close file descriptors while
they may be in use by system calls in
other threads in the same process.
Since a file descriptor may be reused,
there are some obscure race conditions
that may cause unintended side effects.

SEE ALSO

COLOPHON

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